A spray foaming method has been well known as a technique of forming a hard polyurethane foam on site as an insulating material on a surface of a base to be insulated such as a roof, a wall surface, and a floor of a building and a structure such as a warehouse, a barn, and tank facilities that require to retain heat. In the spray foaming method, a technique has been known of using an HFC compound such as 1,1,1,2-tetrafluoroethane (HFC-134a) as a foaming agent in place of a chlorofluorocarbon compound that depletes the ozone layer. However, its cost is very high. A spray foaming method has also been known of using carbon dioxide as a low-cost foaming agent (Patent Documents 1, 2, etc.)
A froth pump is used in a method of interlocking the operation of a foaming machine to the supply of HFC-134a gas from a gas cylinder when discharging a hard polyurethane foam from the foaming machine. That is, the interlocking of them is achieved by connecting an arm of the froth pump to a compression cylinder for a polyol composition that is provided in the foaming machine, and the HFC-134a gas and the polyol composition are mixed together by operating the froth pump by the operation of this compression cylinder when the foaming machine discharges the hard polyurethane foam.
However, when carbon dioxide is used as the foaming agent for example, a pump that sends out carbon dioxide is provided in an apparatus that supplies carbon dioxide. Because of this, the froth pump used for interlocking the supply of carbon dioxide to the operation of the foaming machine cannot be used, and there is a problem that the interlocking of them becomes difficult when carbon dioxide is used as the foaming agent.
[Patent Document 1] Japanese Patent Application Laid-Open No. 2002-327439
[Patent Document 2] Japanese Patent Application Laid-Open No. 2003-082050